paul Posted February 4, 2009 Share Posted February 4, 2009 or does one DNA molecule = all the chromosomes, ie, all the genetic material in our cells? Link to comment Share on other sites More sharing options...
DrDNA Posted February 4, 2009 Share Posted February 4, 2009 no. there are many DNA molecules that make up the sum of genetic material Link to comment Share on other sites More sharing options...
CharonY Posted February 4, 2009 Share Posted February 4, 2009 (edited) In eukaryotes the chromatids consist of a single DNA molecule. So if it is unreplicated it corresponds to the number of chromosomes, but after the S phase the the chromsome consists of two sister-chromatids, so the number of chromsomes remain the same, yet the number of DNA molecule doubles (one for each chromatid). Edit: In prokaryotes one chromosome always consists of a single DNA molecule. Mostly circular, but there are exceptions. Edited February 4, 2009 by CharonY Link to comment Share on other sites More sharing options...
DrDNA Posted February 4, 2009 Share Posted February 4, 2009 In eukaryotes the chromatids consist of a single DNA molecule. So if it is unreplicated it corresponds to the number of chromosomes, but after the S phase the the chromsome consists of two sister-chromatids, so the number of chromsomes remain the same, yet the number of DNA molecule doubles (one for each chromatid). Edit: In prokaryotes one chromosome always consists of a single DNA molecule. Mostly circular, but there are exceptions. .......to clarify further, there are 23 pairs of chromosomes in each (normal) human cell. Plus, we have mitachodrial DNA, which is much like the prokaryotic DNA Charon described above. Link to comment Share on other sites More sharing options...
luminogenics Posted April 26, 2009 Share Posted April 26, 2009 Also, A bacterium may have a chromosome and plasmids. So there is some distinction based on size of the molecule. In some cases the distinction between chromosome and plasmid gets a little fizzy, so like many other concepts it depends on what you mean. Link to comment Share on other sites More sharing options...
vosh Posted April 27, 2009 Share Posted April 27, 2009 or does one DNA molecule = all the chromosomes, ie, all the genetic material in our cells? Hello. First time here. This is interesting because I just started studying this and was just learning about this particular thing. My understanding is that a single (1.8 meter long?) dna molecule is crumpled up to make one chromosome. This would mean that each human nucleus has 46 dna molecules in all. What I'm confused about at the moment is, does this mean that before duplication, the nucleus only has 23 chromosomes? I haven't gotten that much straightened out yet, still reading... Link to comment Share on other sites More sharing options...
CharonY Posted April 27, 2009 Share Posted April 27, 2009 So there is some distinction based on size of the molecule.In some cases the distinction between chromosome and plasmid gets a little fizzy, so like many other concepts it depends on what you mean. Actually the distinction is not based on size, but on the existence of essential functions. In other words, if e.g. non-redundant housekeeping genes are located on a plasmid, it would be considered a chromosome. Vosh, only the gametes have 23 chromomsomes after fertilization (fusion of two gametes) you got 46. However, each chromosomes consists of one (before S phase) or two sister chromatids. Link to comment Share on other sites More sharing options...
vosh Posted April 28, 2009 Share Posted April 28, 2009 (edited) Actually the distinction is not based on size, but on the existence of essential functions. In other words, if e.g. non-redundant housekeeping genes are located on a plasmid, it would be considered a chromosome. Vosh, only the gametes have 23 chromomsomes after fertilization (fusion of two gametes) you got 46. However, each chromosomes consists of one (before S phase) or two sister chromatids. You mean that before that phase (which I'll have to look up, never heard of S phase, seems like everywhere I look there is either a new thing, or the same thing is referred to by a different term...), a single dna molucule, which coiled up is a chromosome, is by itself, but after the S phase it gets joined to another via a centromere? Many thanks. Merged post follows: Consecutive posts mergedor does one DNA molecule = all the chromosomes, ie, all the genetic material in our cells? Well, I googled it, and apparently the term "chromatid" is used to refer to duplicated chromosomes that are joined by a centromere (forming that x shape). So, a dna molecule coiled up is a chromosome (and I think it was called that before it was known to be dna, but someone can sharply correct me on that), when the chromosome duplicates, the two copies are referred to as chromatids, or sister chromatids. When the two are separated, they are then called daughter chromosomes. They're always "dna" and "chromosomes", but there are these different terms for referring to those different situations... I guess is one way to look at it. So, in answer to the question (again - I'm learning by thinking out loud about this), a chromosome is one dna molecule coiled up (so we can see it). When it replicates, it's two chromsomes, two dna molecules, but we call them chromatids, and when they're pulled apart, they're referred to as daughter chromosomes. Hang on... that means that somewhere in there, between replication and division, there are 92 chromosomes. The heck? Thank you for your time. Edited April 28, 2009 by vosh Consecutive posts merged. Link to comment Share on other sites More sharing options...
CharonY Posted April 28, 2009 Share Posted April 28, 2009 They are not called differently, they are just different level of hierarchy. Think of it that way. The chromosome is always the whole structure, regardless whether it consists of one or two chromatids. Likewise during the S-phase (you really need to read up on cell cycles, it is basic knowledge) it is more correct to state that the chromatid replicates rather than that the chromosome duplicates. Because the result is still one single chromosome, only that it consists of two chromatids again. I know wikipedia describes it differently, but in my opinion that description is rather messy. The confusion arises from the fact that chromatids, once separated are referred to as chromosomes, as each cell requires to have the full set of chromosomes. Referring to them as single-chromatid chromsome would be more precise. Use this as starting point and revisit your assumptions once more. Link to comment Share on other sites More sharing options...
GDG Posted April 28, 2009 Share Posted April 28, 2009 When shall we tell him about chromatin? Link to comment Share on other sites More sharing options...
CharonY Posted April 28, 2009 Share Posted April 28, 2009 About 45s after we see smoke emitting from his ears for maximum effect. Link to comment Share on other sites More sharing options...
GDG Posted April 28, 2009 Share Posted April 28, 2009 About 45s after we see smoke emitting from his ears for maximum effect. You set up the webcam; I'll get the stopwatch Link to comment Share on other sites More sharing options...
vosh Posted April 30, 2009 Share Posted April 30, 2009 They are not called differently, they are just different level of hierarchy. Think of it that way. The chromosome is always the whole structure, regardless whether it consists of one or two chromatids. Likewise during the S-phase (you really need to read up on cell cycles, it is basic knowledge) it is more correct to state that the chromatid replicates rather than that the chromosome duplicates. Because the result is still one single chromosome, only that it consists of two chromatids again. I know wikipedia describes it differently, but in my opinion that description is rather messy.The confusion arises from the fact that chromatids, once separated are referred to as chromosomes, as each cell requires to have the full set of chromosomes. Referring to them as single-chromatid chromsome would be more precise. Use this as starting point and revisit your assumptions once more. I see. "Chromosome" refers to the structure we can see under a light microscope of scrunched up dna, either as a single or pair of sister chromatids; is that a good way to say it? Perhaps this is because these are the structures that could be seen via dyes. I'll start from here... I can hear someone saying, "but that website defines a chromosome as a single molecule of DNA...". The websites and the books out there don't seem to have a good starting point. It's good to be able to talk to a phd; someone actually working in the field. Very much obliged. Merged post follows: Consecutive posts mergedWhen shall we tell him about chromatin? Nooooooooooooooooooooooooooo! Link to comment Share on other sites More sharing options...
Angelicous Posted May 3, 2009 Share Posted May 3, 2009 How much does bone marrow play role in producing blood in human being? Link to comment Share on other sites More sharing options...
iNow Posted May 3, 2009 Share Posted May 3, 2009 Angelicous - That quesiton is not really related to this thread at all, but you can probably find your answer here: http://en.wikipedia.org/wiki/Bone_marrow and here: http://en.wikipedia.org/wiki/Red_Blood_Cells Link to comment Share on other sites More sharing options...
arnolp04 Posted May 4, 2009 Share Posted May 4, 2009 don't forget mitochondrial mini-chromosomes in some plants, protists, and 18 of them in the lice genome Link to comment Share on other sites More sharing options...
lucaspa Posted May 12, 2009 Share Posted May 12, 2009 or does one DNA molecule = all the chromosomes, ie, all the genetic material in our cells? Each chromosome is one DNA molecule. We have 23 pairs of chromosomes (1 of the pair from each parent) for 46 chromosomes. So we have 46 DNA molecules per cell. Link to comment Share on other sites More sharing options...
CharonY Posted May 12, 2009 Share Posted May 12, 2009 Actually it depends on the phase. After S (as I mentioned earlier) a single chromsome consists of two DNA (identical) molecules. So double the amount for that time. Link to comment Share on other sites More sharing options...
GDG Posted May 12, 2009 Share Posted May 12, 2009 Plus the several copies of the mitochondrial genome in each mitochondrion. Chloroplasts also have their own genomes, separate from the nuclear DNA. Link to comment Share on other sites More sharing options...
CharonY Posted May 12, 2009 Share Posted May 12, 2009 As well as other extrachromosomal DNA elements. But I think we went full circle here. Link to comment Share on other sites More sharing options...
lucaspa Posted May 13, 2009 Share Posted May 13, 2009 Actually it depends on the phase. After S (as I mentioned earlier) a single chromsome consists of two DNA (identical) molecules. So double the amount for that time. Sigh. Sometimes you guys get a bit too nitpicky. The OP was clearly referring to G1 phase. paul clearly was confused about the relationship between chromosome and DNA molecules. If he knows that one chromosome = one DNA molecule, then paul (when he comes to learning S phase) will clearly realize that copying the chromosome will mean that there are 2 DNA molecules at that point. And, in the mitchondria, one chromosome = 1 DNA molecule there, too. So when paul gets to mitochondrial DNA, he will be able to work it out. Please, try to understand what the question is asking and then answer it in the simplest terms that are still sufficient. That will be a lot more help than going into unnecessary details. Try to focus on the needs of the questioner and not either showing off how much you know or scoring "points" off me when I don't give every possible permutation. Link to comment Share on other sites More sharing options...
iNow Posted May 13, 2009 Share Posted May 13, 2009 Sigh. Sometimes you guys get a bit too nitpicky. This is the second time today you've called the comments of others "nitpicky" (the first time was in response to swansont). I can't help but to chuckle, as I wonder if you've ever read your own posts here which very frequently suffer from that very issue. Link to comment Share on other sites More sharing options...
cetus Posted May 13, 2009 Share Posted May 13, 2009 what does nick picky mean also DNA molecules are in chromosome when a fetus is first devloping in the womb plus the egg and the sperm carry 23 chromosomes each or am i cumfused with something else Link to comment Share on other sites More sharing options...
GDG Posted May 13, 2009 Share Posted May 13, 2009 what does nick picky mean also DNA molecules are in chromosome when a fetus is first devloping in the womb plus the egg and the sperm carry 23 chromosomes each or am i cumfused with something else "Nits" are the eggs laid by lice. The eggs are tiny, and are attached to the base of a hair shaft. Thus, picking at nits (or "nit picking") refers to picking at something insignificant, something that does not matter. DNA is normally in the form of euchromatin: it only condenses into chromosomes when it is time for the cell to divide. "Chromosome" refers to the condensed version, but euchromatin and chromosomes contain the same DNA, just different proteins are attached to wind it up. The egg and sperm (of humans) each have 23 chromosomes. Link to comment Share on other sites More sharing options...
Mr Skeptic Posted May 14, 2009 Share Posted May 14, 2009 Each chromosome is one DNA molecule. We have 23 pairs of chromosomes (1 of the pair from each parent) for 46 chromosomes. So we have 46 DNA molecules per cell. Technically, a double-stranded DNA is really two complementary DNA molecules. So then we have 92 DNA molecules composing our chromosomes, as 23 pairs of double-stranded DNA. Sigh. Sometimes you guys get a bit too nitpicky. As GDG said, "Nits" are the eggs laid by lice. The eggs are tiny, and are attached to the base of a hair shaft. Thus, picking at nits (or "nit picking") refers to picking at something insignificant, something that does not matter. So its only nit picking in the metaphorical sense Link to comment Share on other sites More sharing options...
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